Dear Mark: Is There No Upper Limit to Endurance Training?

Yesterday, I linked to a study[1] showing that the beneficial effects of high levels of cardiorespiratory fitness—the kind you build with cardio/endurance training, HIIT, and sprints—have no upper limit. At first glance, this study appears to bust the “myth” of chronic cardio and the U-shaped curve of endurance training and prove that the more you train, the longer you’ll live. This appears to run counter to some of my central claims—that too much mid-to-high intensity endurance exercise leads to burnout, health issues, and diminishing returns.

A commenter wrote a great comment that got me wondering:

As far as “the more exercise the better” study I wonder if folks who had to drop out of long distance cardio training due to injuries or cortisol driven exhaustion are considered in the equation? In other words, if you can tolerate chronic cardio you may live longer, otherwise it might break you down. Everyone has a sweet spot for exercising is my gut feeling and you have to “listen to your body”. I still like the primal mantra along the lines of (if I may be so presumptuous as to paraphrase Mark) “walk a lot, do sprints once a week, lift heavy things once or twice a week, spend time outdoors, take part in sports or recreational activities that are fun for you”.

What do I think is going on? How do the results of this paper jibe with my take on Chronic Cardio?

First off, we have to acknowledge the basic structure of the study.

This study didn’t actually measure “hours spent training.” They gave subjects treadmill tests (stress tests) to determine their cardiovascular fitness, then divided everyone into different tiers of fitness based on the results. In fact, the authors of the study criticized the shortcomings of previous studies which used self-reported training data instead of objective measurements of cardiorespiratory fitness like the treadmill test. This makes the study far more accurate and useful. It also means you can’t make any ironclad proclamations about the connections between hours spent training and longevity. You can certainly make inferences—people who had better cardio fitness probably spent more time training to get it—but there are other interpretations. All you can say for certain is that higher levels of cardio fitness predict greater longevity.

I don’t see how anyone could argue with that. Of course being fitter is better.

But my criticism of chronic cardio isn’t a criticism of cardiovascular fitness. It’s a criticism of how most people go around obtaining that fitness—by destroying their bodies.

That doesn’t have to happen anymore. Tons of top guys these days are finally figuring out that you don’t have to log as many laps/miles/etc as possible to maximize your performance, but that wasn’t always the case. I grew up convinced that the more miles I ran, the healthier I’d be. That’s how I did it back in my marathon and triathlon days, and it almost destroyed me and an entire generation of my peers.

You can train twice as much as the next guy yet have worse fitness, either because you’re not training intelligently, you’re overtraining and hampering the adaptive process, or you’re not sleeping. That’s chronic cardio. You can train less and get better results, if you’re optimizing your recovery, nutrition, and sleep. That’s Primal Endurance[2].

As for these subjects, there is some serious genetic confounding occurring. Those dudes with elite fitness levels well into their 70s are often a different breed. They’re hard to kill. They’re tough. They can withstand the discomfort of grueling mile after mile. What other types of discomfort can they bear and even grow from? They’re just more robust than the average 70-year-old. It may not be the elite training itself that’s making them resist death. It’s just as likely they have the genetic capacity to excel in endurance training, and even if they didn’t exercise they’d still live longer than average.

There’s also the healthy user bias. The kind of lifestyle regular exercisers follow emphasizes sleep, plenty of rest and recuperation, smart supplementation and nutrition, and all sorts of other things that are also linked to longer, better health.

This paper makes a strong case for using something like Primal Endurance[2] to build great cardiorespiratory fitness without risking chronic cardio territory.